Field
The present invention relates to a micromechanical device.
Description of the Related Art
Micro-Electro-Mechanical Systems, or MEMS, can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. Since MEMS devices are created with the same or similar tools used to create integrated circuits, micromachines and microelectronics can even be fabricated on the same piece of silicon. MEMS structures can be applied to quickly and accurately detect very small changes in physical properties.
While being very small in size, MEMS structures have different and unique failure mechanisms when compared to similar macroscopic structures.
One failure mechanism known for MEMS devices is stiction, which means adhesion of structural components to one another or to a substrate, material from which the structure is made of. Stiction may be prevented for instance by using anti-stiction coatings or forming surface structures such as for example bumps at the colliding surfaces so that touching surface area is reduced.
Another known failure mechanism is breakage, such as cracking or fracture of MEMS structures due to impact. A single, hard impact may cause cracking or fracture of a MEMS structure, or several repeated impacts may cause fatigue of MEMS structure which eventually leads to breaking of the structure.
US2012/0280591 presents a MEMS device with movable element having a secondary structure having a secondary mass and a spring interconnected with the secondary mass and the movable element. When the device is subject to mechanical shock, the secondary structure causes the secondary mass to impact the movable element so that it's likely dislodged if stuck after the impact. A problem relating to the prior art US2012/0280591 is that although the secondary structure enables relief from sticking problem, the movable mass may be damaged due to the impact caused by a shock.
US201426013 presents an elastic bump for reducing impact force caused to the MEMS moving structure upon encountering a shock, thus reducing risk of structure breakage. Secondary, non-flexible bump stops are implemented in the proof-mass.
What is needed is an improved structure for a MEMS device that can both reduce risk of structure cracking and have a mechanism to prevent sticking of the movable proof-mass.